One example of a conventional refrigeration device that includes a vapor compression refrigeration circuit is an air conditioner that is employed to provide air conditioning for buildings or the like. This type of air conditioner primarily includes a heat source unit, a plurality of user units, and a refrigerant gas junction line and a refrigerant liquid junction line that serve to connect these units together. The refrigerant gas junction line and the refrigerant liquid junction line of the air conditioner are positioned so as to connect the heat source unit and the plurality of user units, and thus the lines are long and have a complex line shape that includes many curves and branches along the length thereof. Because of this, when the air conditioner is to be renovated, there will be many occasions in which only the heat source unit and the user units are renovated, and the refrigerant gas junction line and the refrigerant liquid junction line of the preexisting device are left in place.
In addition, many conventional air conditioners use an HCFC refrigerant such as R22. The lines, devices, and the like that form the refrigerant circuit of this type of air conditioner have a strength that corresponds to the saturation pressure of the operating refrigerant at a normal temperature. However, because environmental problems are being taken into consideration in recent years, there are continuing efforts being made to replace HCFC refrigerants with HFC or HC refrigerants. Because of this, air conditioners that are employed to air condition buildings or the like are being renovated by replacing the preexisting heat source unit and the user units that use R22 as the operating refrigerant with devices that use HFC refrigerants such as R407C that approximate the saturation pressure characteristics of R22 as the operating refrigerant, and reusing the refrigerant gas junction line and the refrigerant liquid junction line of the preexisting air conditioner.
On the other hand, it is desirable for the aforementioned air conditioner to have improved refrigeration efficiency and reduced power consumption. In order to meet these needs, using HFC refrigerants such as R410A and R32 that have saturation pressure characteristics that are higher than those of R22 or R407C has been considered. However, if one attempts to use a refrigerant such as R410A or R32 as the operating refrigerant, not only will the heat source unit and the user units have to be replaced, but the refrigerant gas junction line and the refrigerant liquid junction line will also have to be replaced with lines that have strengths corresponding to the saturation pressure characteristics thereof, and thus the task of installing the air conditioner will be more burdensome than before.
An example of an air conditioner that is capable of solving these types of problems is the air conditioner disclosed in Japanese Published Patent Application No. 2002-106984. This air conditioner has a refrigeration circuit that includes a compressor, a heat source side heat exchanger, and user side heat exchangers, and a heat source side auxiliary heat exchanger that is connected in parallel to the heat source side heat exchanger. When the refrigerant pressure on the discharge side of the compressor of the air conditioner increases during cooling operations, the refrigerant on the discharge side of the compressor is introduced into the heat source side auxiliary heat exchanger and condensed, and thus the refrigerant pressure of the refrigerant circuit between the discharge side of the compressor and the user side heat exchangers (including the refrigerant liquid junction line) can be decreased. This allows the heat source unit and the user units to be replaced with those that use R410A as the operating refrigerant, and allows the refrigerant liquid junction line of the preexisting air conditioner that employs R22 and the like to be left in place and reused.
However, the heat source side auxiliary heat exchanger of the aforementioned air conditioner is provided in order to adjust the refrigerant pressure of the refrigerant circuit between the heat source side heat exchanger and the user side heat exchangers that includes the refrigerant liquid junction line during cooling operations, and is not designed to adjust the refrigerant pressure of the refrigerant gas junction line during heating operations. Because of this, it is assumed that, during heating operations, the air conditioner will be operated so as to maintain the heating ability in each user unit, while making the discharge pressure of the compressor lower than the maximum allowable pressure of the refrigerant gas junction line. More specifically, in order to maintain heating ability in each user unit, the air conditioner must be operated so that the refrigerant gas temperature on the discharge side of the compressor is kept at a predetermined temperature, and the discharge pressure of the compressor is made lower than the maximum allowable pressure of the refrigerant gas junction line.
However, because R410A has saturation pressure characteristics that are higher than those of R22 and the like, when the intake temperature of the compressor is the same, only a discharge temperature that is lower than the discharge temperature obtained with R22 and the like can be obtained, even if the pressure is raised by means of the compressor to the same as the discharge pressure. Thus, to the extent possible, heating operations must be performed with the discharge pressure of the compressor raised to near the maximum allowable pressure of the refrigerant gas junction line in order to increase the refrigerant temperature. On the one hand, when the air conditioner is operated to raise the discharge pressure of the compressor to near the maximum allowable pressure of the refrigerant gas junction line, superior pressure control will be needed that is responsive to pressure increases, particularly rapid pressure fluctuations such as changes in heating load.
On the other hand, it is desirable for the aforementioned air conditioner to have improved refrigeration efficiency and reduced power consumption. In order to meet these needs, using HFC refrigerants such as R410A and R32 that have saturation pressure characteristics that are higher than those of R22 or R407C has been considered. However, if one attempts to use a refrigerant such as R410A or R32 as the operating refrigerant, not only will the heat source unit and the user units have to be replaced, but the refrigerant gas junction line and the refrigerant liquid junction line will also have to be replaced with lines that have strengths corresponding to the saturation pressure characteristics thereof, and thus the task of installing the air conditioner will be more burdensome than before.
In addition, as noted above, not only will there be situations in which the preexisting refrigerant gas junction line and the refrigerant liquid junction line of an air conditioner that used R22, R407C, and the like will be left in place and reused and a new heat source unit and user units that use refrigerant such as R410A, R32, and the like having saturation pressure characteristics that are higher that those of R22 and R407C will be used with the preexisting lines, but there will also be situations in which refrigerant gas junction lines and the refrigerant liquid junction lines that have saturation pressure characteristics that are higher than R410A, R32, and the like cannot be prepared, even when a new air conditioner is to be installed. In this situation as well, because the air conditioner is operated to raise the discharge pressure of the compressor to near the maximum allowable pressure of the refrigerant gas junction line, superior pressure control will be needed that is responsive to pressure increases, particularly rapid pressure fluctuations such as changes in heating load.